Wood Burning Hot Tub Heater

Our house has all its electric power generated on-site, so an electrically heated spa pool was just not feasible. So Allan designed a wood-burning heater, made of stainless steel that could sit inside a cedar hot tub to heat the water.

This wood-burning hot tub heater consists of a firebox joined to a secondary burn chamber with internal tubes to provide more hot surface area. The flue is in three parts and the lower part, which is attached to the heater, has a water jacket.

The firebox is top loading and burns downwards, the flames passing into the large secondary burn chamber where it completely double burns and finally exits the chimney with NO visible smoke

The heater has been carefully designed to maximise the heat transfer from the heater to the water in the hot tub.

Pricing

Wood burning heater + Flue
$1380 + GST

Cedar Hot Tub
Price on request

Water circulating pump and filter
Price on request

Protective wooden fence
Price on request

Call us on 027 279 3483

The heater is bolted to the seat inside the hot tub so that the top of the firebox will be just above the level of the water in the hot tub when the tub is filled.

(This picture shows one of the earlier heaters with no water jacket on the flue.)

With a good supply of dry wood, a fire can be started in the firebox. The secondary burn chamber allows hot air from the firebox to come into close contact with the water in the hot tub. The water jacket around the bottom of the flue decreases heat loss and increases heat transfer from the hot air to the water.

A wooden fence can be used to protect people sitting inside the hot tub from the heater.
It is actually possible to sit in the hot tub with no fence as most of the heater is at or near the water temperature.

A small pump is used to circulate water through a filter and to move the tub water around. Our 1800 litre hot tub takes about 6 hours to heat to 37°C from cold. If the heater is used every day, it will reheat in about an hour and needs only about an armful of dry gorse. Perhaps I should say that we have a good supply of mature gorse. It much prefers dry wood and we also burn our ‘burnable’ rubbish which includes citrus skins.This is a brilliant way to have a cosy hot tub on a cold, dark night – using next to no electricity. You are very welcome to come and try it for yourselves.